1. Technical Field
The present invention relates to a projection-type vehicular headlamp.
2. Description of the Related Art
Generally, a projection-type vehicular headlamp is structured such that a projection lens is disposed on an optical axis that extends in vehicle's longitudinal direction, while a light source is disposed to the rear of a rear-side focal point of the projection lens, and light from the light source is reflected toward the optical axis by a reflector. When forming a low-beam distribution pattern from a projection-type vehicular headlamp, a portion of reflected light from a reflector in the vicinity of the rear side focal point of the projection lens is blocked by a shade disposed at an upper end edge near the optical axis. A predetermined cut-off line is thus formed on an upper end portion of the low-beam distribution pattern.
Unexamined Japanese Patent Publication No. 2001-229715 describes a projection-type vehicular headlamp that is structured with a first additional reflector disposed in front of and obliquely below a light source, and a second additional reflector disposed above the light source adjacent to the reflector so as to sequentially reflect light from the light source with the first additional reflector and the second additional reflector. Furthermore, the projection-type headlamp is structured with a shutter disposed between the first additional reflector and the second additional reflector so as to make it possible to prevent reflected light from the first additional reflector from becoming incident to the second additional reflector.
In order to improve visibility of a road surface in front of the vehicle using light radiated from the vehicular headlamp, it is desirable for a plurality of various light distribution patterns to be formed depending on a vehicle's traveling condition, even for identical low-beam distribution patterns.
In the vehicular headlamp described in Unexamined Japanese Patent Publication No. 2001-229715, opening and closing the shutter allows for the formation of a low-beam distribution pattern in two modes: a normal low-beam distribution pattern mode, and a low-beam distribution pattern mode wherein a light distribution pattern formed by light sequentially reflected from the first and second additional reflectors is added to the normal low-beam distribution pattern. However, the following problems exist.
first problem exists in the vehicular headlamp described in Unexamined Japanese Patent Publication No. 2001-229715 whereby light is reflected twice by the first and second additional reflectors. This twice reflected light is further radiated forward without passing through the projection lens, thus leading to the inability to control the radiated light with high precision. An additional problem exists whereby the light distribution pattern formed by light sequentially reflected by the first and second additional reflectors differs in quality from the low-beam distribution pattern formed by light from the light source that is reflected by the reflector and which passes through the projection lens. Both the inability to control radiated light with high precision and the noticeable difference in the quality of the light distribution pattern when switching between modes are problematic for obvious reasons. Similar problems are also found in prior art headlamps when forming a high-beam distribution pattern, or the like.